It’s the bit we rarely see in fairytales; the heroine bags her Prince Charming, plants a kiss on his lips, and skips off into the sunset.
But how do we know if Cinderella managed to make things work?
And, more importantly, how do we achieve our very own happily ever after?
Well, according to mathematician Hannah Fry, it all comes down to a simple formula of negative and positive perceptions.
That looks pretty complex, we know, but the author of The Mathematics Of Love managed to break things down for us pretty well.
She explains: "In relationships where both partners consider themselves as happy, bad behaviour is dismissed as unusual."
For example, you would assume that your partner’s grumpiness is due to stress at work or a bad night's sleep.
"In negative relationships, however, the situation is reversed," she writes.
"Bad behaviour is considered the norm."
More simply, you are more likely to assume your partner’s grumpiness is "typical," due to their "selfishness" or other negative personality trait.
Basically, successful relationships are ones where couples give each other the benefit of the doubt and work together.
Relationships that are less likely to last are ones where couples get so fed up with each other during an argument that they don't bother talking it out.
Maths = the ultimate relationship guru?
Yup, we think so, too.